Several new features recently emerging in radio communication devices, such as cellular phones, and personal digital assistants require the storage of large amounts of speech. For example, there are application areas of voice memo storage and storage of voice tags and prompts as part of the user interface in voice recognition capable handsets. Typically, recent cellular phones employ standardized speech coding techniques for voice storage purposes.
Standardized coding techniques are mainly intended for real time two-way communications, in that, they are configured to minimize buffering delays and achieving maximal robustness against transmission errors. The requirement to function in real-time imposes stringent limits on buffering delays. Clearly, for voice storage tasks, neither buffering delays nor robustness against transmission errors are of any consequence. Moreover, the timing constraints and error correction require higher data rates for improved transmission accuracy.
Although speech storage has been discussed for multimedia applications, these techniques simply propose to increase the compression ratio of an existing speech codec by adding an improved speech-noise classification algorithm exploiting the absence of coding delay constraint. However, in the storage of voice tags and prompts, which are very short in duration, pursuing such an approach is pointless. Similarly, medium-delay speech coders have been developed for joint compression of pitch values. In particular, a codebook-based pitch compression and chain coding compression of pitch parameters have been developed. However, none of these approaches exploit perceptual criteria for a given target speech quality to further improve data compression efficiency.
Therefore, there is a need for a codec with a higher compression ratio (lower data rate) than conventional speech coding techniques for use in dedicated voice storage applications. In particular, it would be an advantage to use perceptual criteria in a dedicated speech codec for storage applications. It would also be advantageous to provide these improvements without any additional hardware or cost.
The exemplification set out herein illustrates a preferred embodiment of the invention in one form thereof, and such exemplification is not intended to be construed as limiting in any manner.